1. Field of the Invention
The invention relates to a single-part cooling channel piston for a combustion engine with a piston head of forged steel, comprising a combustion bowl in the piston crown, a ring wall with a ring belt and an all-round closed cooling channel level with the ring belt. The piston skirt is connected to the pin bosses attached to the piston head.
2. The Prior Art
Generic single-part cooling channel pistons are known for example from European Patent No. EP 0 799 373 B1 or DE 100 13 395 C1. In the cooling channel pistons described therein, a piston blank is manufactured by forging an annular recess and the cooling channel, open to the bottom, is provided by metal-cutting machining methods, and then the outer contour of the piston is finish-machined. The axial height of the annular recess corresponds in EP 0 799 373 B1 at least to the axial height of the cooling channel. This is necessary since a hook-like turning tool is inserted into the recess for manufacture of the cooling channel open to the bottom and the cooling channel must be hollowed out into its required form by appropriate axial and radial infeed.
The drawback with these pistons is that the height of the hook-like turning tool determines the achievable cooling channel height and hence the quantity of heat to be dissipated from the piston crown as a consequence of high wall thicknesses. To increase the cooling channel height or to reduce the wall thickness between the cooling channel and the piston crown, the recess for insertion of the turning tool would have to be increased, which would however entail an unwelcome increase in the height of the piston.
On the other hand, the piston stability would decrease as a result of the aforementioned reduced wall thickness. Therefore, the above manufacturing methods and piston designs are not suitable for improvement of the piston with respect to its height or its stability for the high ignition pressures and temperatures as encountered in modern diesel engines.
It is therefore an object of the present invention to provide an improved piston concept for a single-part cooling channel piston with which inexpensive manufacture of a low-height piston is assured and with which piston deformation due to the effects of high gas pressures and temperatures can be effectively countered.
This object is achieved by piston having a cooling channel formed in the piston head with holes spread over its circumference towards the piston crown, with the holes spaced such that the piston material present between such holes forms supporting ribs for the piston crown.
With a piston manufactured in this way, at least part of the cooling channel can be formed closer towards the piston crown or combustion bowl and nevertheless has excellent form stability plus a low piston height. In addition, the arrangement of the supporting ribs effects a kind of chamber formation inside the cooling channel, i.e. creates shaker areas, whereby a prolongation of the dwell time of the cooling oil is achieved and hence an improved heat dissipation of the piston areas to be cooled. In particular, the cooling effect can be further improved by a higher number of holes in those areas of the cooling channel in which the combustion radiation impacts the piston crown.